Many of the helicopters being operated today embody a dual-engine powerplant system. A dual-engine powerplant system enhances the normal flight capabilities of a helicopter, thereby increasing the utility of the helicopter for revenue flight operations. In addition, a significant feature inherent in a dual-engine helicopter is the capability of the dual-engine powerplant system to provide sufficient power to facilitate continued flight operations in safety, particularly take offs and landings (take offs and landings being the most critical segments of the helicopter flight envelope), in the event of a one engine inoperative (OEI) condition, e.g., a single engine failure.
Since the OEI condition is statistically a low-occurrence event, the engines of a helicopter dual-engine powerplant system are designed primarily for dual-engine flight operations. That is, each engine is designed to specific power limits or ratings for dual-engine flight operations, e.g., a startup power rating, a take off power rating, a maximum continuous power rating (maximum power settings at which the engines may be continuously operated during dual-engine flight operations without incurring damage), a normal cruise power rating (power settings slightly lower than maximum continuous power rating that are typically established to comply with the engine maker's warranties), a 10-second transient power rating, and a 20-second transient power rating. During dual-engine flight operations, therefore, the helicopter is operated in such a manner that the design power ratings of the engines are not exceeded. In the sophisticated helicopters of today, the operation of the powerplant system is primarily controlled by a computer system (discussed in further detail hereinbelow), and such an engine computer control system typically includes protective logic routines (in the form of hardware, firmware, software, and/or combinations thereof) that automatically prevent the engine design power ratings from being exceeded during dual-engine flight operations.
A dual-engine helicopter that experiences an OEI condition, especially during a take off or landing, is subject to a potentially hazardous flight condition since the normal design power ratings of the single operative engine do not provide sufficient power for the safe operation of the helicopter under such a circumstance. Aviation regulatory authorities, therefore, have established general overdesign criteria for the powerplant system of a dual-engine helicopter to ensure that the helicopter can be safely operated utilizing a single operative engine during OEI flight operations. These criteria have resulted in the overdesign of the helicopter powerplant system so that a single operative engine is capable of providing the requisite emergency or OEI power necessary for safe helicopter flight operations during an OEI condition.
The helicopter powerplant system is overdesigned so that the single operative engine has the capability to provide a 30-second OEI power rating, a 2-minute OEI power rating, and a maximum continuous OEI power rating. These OEI power ratings are higher than the normal design ratings of the powerplant system, and therefore, are intended for use only during an OEI condition.
The 30-second OEI power rating was established to ensure that the single operative engine provides a sufficient margin of power so that a dual-engine helicopter can continue a take off flight profile to a take off safety speed (V.sub.toss) in relative safety while avoiding obstacles such as trees, an elevated platform, and/or the ground. The engine computer control system of the powerplant system is operative, by means of default logic (implemented in the form of hardware, firmware, software, and/or combinations thereof) to cause the single operative engine to automatically default to the 30-second OEI power rating in the event of an OEI condition. The 30-second OEI power rating is of such magnitude that there is a statistically-high probability that the single operative engine may be subjected to some degree of damage, e.g., burnout, during OEI flight operations the engines of a dual-engine powerplant system are certified for up to three applications of the 30-second OEI power rating in a single flight!.
The 2-minute OEI power rating was established to ensure that the single operative engine provides a sufficient margin of power so that a dual-engine helicopter operating at V.sub.toss can initiate and maintain an ascending flight profile at a sufficient vertical speed, e.g., 100 feet/minute, to reach a safe cruising altitude within two minutes after implementation of the 2-minute OEI power rating without resort to the 30-second OEI power rating. The maximum continuous OEI power rating was established to ensure that the single operative engine provides a continuous margin of power, i.e., use of the maximum continuous OEI power rating cannot be time limited, so that the dual-engine helicopter can continue OEI flight operations at the safe cruising altitude to reach a distant landing site. For example, in the case of an OEI take off flight profile from an elevated offshore platform, the most propitious landing site is most probably the nearest adjacent landmass. For a most efficacious OEI control system, the 30-second OEI power rating, the 2-minute OEI power rating and the maximum continuous OEI power rating should be manually selectable by the pilot.
The aviation regulatory authorities also require that an OEI monitoring system be provided for OEI flight operations that has the functional capability to provide the pilot with continual cognitive awareness of which OEI power rating, i.e., the 30-second OEI power rating, the 2-minute OEI power rating, or the maximum continuous OEI power rating, the single operative engine of a dual-engine helicopter is being operated under, and when the allowable time for usage of the 30-second and 2-minute OEI power ratings has elapsed. The OEI monitoring system should be ergonometrically configured to optimize the functional task of visually monitoring critical OEI parametric information and the functional task of visually monitoring OEI flight operations. In addition, the OEI monitoring system should be ergonometrically optimized for visual efficiency, i.e., to present a maximum of OEI parametric information with minimal visual scanning by the pilot. Furthermore, the OEI monitoring system should have the functional capability of readily alerting the pilot to status changes with respect to displayed OEI parametric information.